1. Field of the Invention
The present invention relates to a disc-shaped record medium preferable as a writable optical disc such as a write once optical disc (CD-R), a rewritable optical disc (CD-RW), and a mini disc (MD), a method for manufacturing the same, and an apparatus for manufacturing the same.
Specifically, in the present invention, a simulation is conducted at the time of writing pre-format addresses in an original disc for the disc-shaped record medium. In the simulation, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand between the pre-format address in the target frame and the pre-format address in the other frame next to the target frame. Based on the result of the simulation, the pregrooves and the lands are defined on the original disc. In thus-formed original disc, there is no problem in preventing crosstalk between adjacent pregrooves. By use of the original disc, it is possible to manufacture a writable optical disc having high storage density.
2. Description of the Related Art
In recent years, as information media for editing and recording audio information in such a manner as to suit the preferences of listeners, writable optical discs such as write once optical discs (CD-R) and rewritable optical discs (CD-RW) standardized in ISO/IEC13490-1 are increasingly used. In each of these optical discs 10, as shown in FIG. 1A, grooves 1 for guiding a light beam (hereinafter, referred to as pregrooves) are formed, and a positioning method referred to as a tracking servo is employed. The tracking servo is a mechanism where pits and projections constituting lands 2 formed on both sides of each pregroove 1 are detected to decide the position of an optical pickup, so that the desired pre-format address is accurately irradiated with a laser beam.
Sloped surfaces of the land, which coincide to side surfaces of the pregroove 1, is formed with a slight wobble in the form of sine wave in-phase with each other as shown in FIG. 1B. The wobble signal indicating the wobble component has been subjected to FM modulation. In the wobble signal, time axis information indicating the position on the optical disc 10, and a recommended value of the power of the laser beam optimum for recording, etc. are encoded.
The time axis information is referred to as ATIP (absolute time in pregroove) information, and is written as an absolute time in the signal recording region (i.e. a program region) of the optical disc 10 along a direction from the starting point at its inner peripheral side toward its outer peripheral side. The ATIP information is written in the processing of the CD-R and CD-RW. The ATIP information is written in the optical disc 10 such as CD-R and CD-RW in a modulation mode referred to as bi-phase modulation mode. In this mode, a baseband modulation is conducted where, depending on whether the waveform of the last pulse signal constituting the error correction information of the immediately preceding pre-format address ends at a high level or low level, the pre-format address in the next frame is connected without being inverted, or the pre-format address is inverted and connected.
The ATIP information is written, for example, in the side surfaces Us, Ut of the pregroove 1 between two lands 2a, 2b shown in FIG. 1B. That is, the ATIP information is written in the side surface Us of the land 2a located at the inner peripheral side of the pregroove 1 in which data is recorded, and in the side surface Ut of the land 2b located at the outer peripheral side of the pregroove 1 in such a manner that the ATIP information written in the side surface Us is synchronous to the ATIP information written in the side surface Ut.
Therefore, the ATIP information can be read as a wobble signal by detecting the wobble formed in the land 2b located at the outer peripheral side by the preceding side spot 3. The preceding side spot 3 is a light beam preceding a main spot 4 which is a light beam for recording information. The circle broken double lines in FIG. 1B show spot diameters of the light beam irradiated to the optical disc having a standard density. The broken circle line in FIG. 1B shows a spot diameter of a light beam for an optical disc with a standard density. The circle broken double lines shows a light beam of which irradiation diameter is relatively enlarged as the pregrooves are formed so as to be closer to each other in proportional to the increase in a storage density of the disc-shaped record medium 10. This problem arises because there is a limitation on enlarging the spot diameters of the light beam.
A wobble formed in the land 2a located at the inner peripheral side is detected as a wobble signal by the posterior side spot 5. The wobble signal is produced in such a manner that its center frequency becomes 22.05 kHz for example, when the optical disc 10 is rotated at a standard velocity (CLV) of a compact disc (CD). One sector of the ATIP information is constituted in such a manner as to coincide to one data sector after the signal is recorded. Therefore, at the time of recording information, the pre-groove 1 is irradiated with a light beam with a predetermined intensity and information is written therein while the sector of the ATIP information is synchronous with the data sector.
In the bi-phase modulation mode according to a conventional example, when the error correction information for the bi-phase signal of the immediately preceding pre-format address ends at high level, a baseband modulation is conducted in such a manner that the bi-phase signal of the pre-format address having synchronous information starting at low level is connected. Contrary to this, when the error correction information for the bi-phase signal of the immediately preceding pre-format address ends at low level, a baseband modulation is conducted in such a manner that the bi-phase signal of the pre-format address having synchronous information starting at high level is connected.
If pre-format addresses are written in the bi-phase modulation mode as it is without conducting any processing in the recent situation where the lands 2a, 2b are arranged at narrower pitches P in accordance with the increase in the storage density of the optical disc 10 (hereinafter, referred to as a disc-shaped record medium in some cases), the light beam of which irradiation diameter is relatively enlarged as the pregrooves are formed so as to be closer to each other is applied across the adjacent pregrooves (see FIG. 1B). In this case, there arises much fear that crosstalk is generated. The crosstalk causes phase modulation to create jitter.
As a result, when the bi-phase signal constituting the target pre-format address at the reading point is superimposed on the bi-phase signal of the other pre-format address adjacent to the target pre-format address, there is a large difference in phases therebetween. Larger jitter is created as the period of high level is shorter.
The present invention has been conducted to solve the above-described problems of the prior arts, and the objective thereof is to provide a disc-shaped record medium usable for producing a writable optical disc which has high storage density and is capable of preventing crosstalk generated in adjacent pregrooves, a method manufacturing the same, and an apparatus for manufacturing the same.
The above-described problems can be solved by a disc-shaped record medium in which pre-format addresses are written along its grooves for guiding a light beam. In the disc-shaped record medium, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand. The dummy information is recorded between the pre-format address in the target frame and the pre-format address in the other frame next to the target frame.
According to the disc-shaped record medium of the present invention, phase modulation caused by the crosstalk between adjacent pregrooves can be prevented even if a light beam is applied across the adjacent pregrooves when an arbitrary pre-format address is designated to write information in the pregroove, or the information is read from the pre-format address. As a result, a jitter can be suppressed. With this arrangement, it becomes possible to provide a rewritable optical disc such as a CD-R and CD-RW having high storage density in which the pregrooves 1 are arranged at pitches narrower than the irradiation diameter of the light beam.
A method for manufacturing a disc-shaped record medium of the present invention is a method in which pre-format addresses are written in its grooves for guiding a light beam, including the steps of: conducting a simulation where, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand between the pre-format address in the target frame and the pre-format address in the other frame next to the target frame; producing a control signal for groove formation based on the result of the simulation; and causing a light beam with a predetermined intensity to oscillate on the original disc in its inner and outer peripheral direction while the original disc is rotated at a predetermined linear velocity to define pregrooves in the shape of pits and lands in the shape of projections on the original disc, thereby writing the pre-format addresses in the original disc.
According to the method for manufacturing a disc-shaped record medium of the present invention, at the time when the disc-shaped record medium in which pre-format addresses are written is manufactured, a simulation is conducted where, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand between the pre-format address in the target frame and a pre-format address in the other frame next to the target frame.
With this arrangement, a control signal for groove formation intended for the case where an arbitrary pre-format address is designated and information is written in the pregroove, and the information is read from the address is produced. The control signal for groove formation is capable of removing the influence of crosstalk generated at the time when a light beam is applied across the adjacent pregrooves. By writing the pre-format addresses based on the control signal, it is possible to manufacture a write once optical disc having high storage density in which the pregrooves are arranged at pitches narrower than the irradiation diameter of the light beam with excellent reproducibility.
According to an apparatus for manufacturing a disc-shaped record medium in which pre-format addresses are written along its grooves for guiding a light beam of the present invention, including: a data processor for conducting a simulation where, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand between the pre-format address in the target frame and the pre-format address in the other frame next to the target frame; a signal generator for producing a control signal for groove formation based on the result of the simulation by the data processor; and an information writer for causing a light beam with a predetermined intensity to oscillate on the original disc in its inner and outer peripheral direction while the original disc is rotated at a predetermined linear velocity to define pregrooves in the shape of pits and lands in the shape of projections on the original disc, thereby writing the pre-format addresses in the original disc.
According to an apparatus for manufacturing a disc-shaped record medium of the present invention, at the time when the disc-shaped record medium in which at least pre-format addresses are written in its grooves for guiding a light beam, the data processor conducts a simulation where, in order that the crosstalk caused by the coexistence of an arbitrary pre-format address with the other pre-format address adjacent to the arbitrary pre-format address in the inner and outer peripheral direction at the reading point of the arbitrary pre-format address, specific dummy information for timing adjustment is inserted beforehand between the pre-format address in the target frame and the pre-format address in the other frame next to the target frame. After that, the signal generator generates a control signal for groove formation based on the result of the simulation conducted by the data processor.
For example, the control signal for groove formation is produced in such a manner that, when the waveform of the last pulse signal constituting the error correction information of the immediately preceding pre-format address ends at high level, a waveform of pulse signal constituting dummy information for timing adjustment is connected so that a waveform of a pulse signal constituting a pre-format address in the next frame including synthetic information starting at high level or low level is connected.
The control signal is input into the information writer. In the information writer, based on the control signal, a light beam with a predetermined intensity is caused to oscillate on the original disc in its inner and outer peripheral direction. At the same time, the original disc is rotated at a predetermined linear velocity. In this manner, the pregrooves and lands are defined on the original disc. As a result of these processes, pre-format address are written in the original disc.
With this arrangement, it is possible to manufacture a disc-shaped record medium free from the influence of crosstalk even if a light beam is applied across the adjacent pregrooves. In addition, it is possible to manufacture a writable optical disc having high storage density in which the pregrooves are arranged at pitches narrower than the irradiation diameter of the light beam.